1. Field of the Invention
The present invention relates to lightning suppression attenuators. More particularly, the present invention relates to lightning suppression devices that can be used so as to cushion the effects of lightning strikes. More particularly, the present invention relates to lightning suppression devices that prevent the effects of lightning from affecting equipment connected to coaxial cable extending to antennas.
2. Description of Related Art
Lightning conceivably may have provided humankind with a first source of fire, but lightning has otherwise been a destructive force throughout human history. Strategies and apparatus for reducing the likelihood of damage by lightning are fairly old, including, for instance, lightning rods that have been use for approximately 200 years. While the use of such rods and other precautionary steps and safety devices reduce the damage and injury that would otherwise result from lightning today, it remains an enormously dangerous natural phenomenon that claims hundreds of lives worldwide every year and destroys a substantial amount of property. Somewhat paradoxically, advances in other areas of technology have increased, rather than diminished, the damaged caused by lightning. This is because relatively low voltage and current levels can damage integrated circuits and other modem electronic components, with the result that many electronic devices are more susceptible to lightning damage today than ever before. Many devices to which microprocessors technology has been added are more susceptible to lightning damage as a result of such improvements. Additionally, lightning is capable of inducing substantial currents not only in electrical circuits directly struck by it but also in circuits located within the magnetic field induced by a nearby lightning strikes, giving each strike enormous destructive potential.
One of the most common areas of lightning strikes are large telecommunications and camera towers that extend upwardly from the earth. Typically, such towers include an electronic device at the top which serves to transmit or receive information. Since lightning will follow a path of least resistance on its way to the earth, the towers are very attractive to lightning. It is well known that lightning is particularly attracted to areas of positive ions and is repelled by areas of negative ions. Since the electronic devices at the top of towers often operate on AC power, an attractive source of positive ions is generated at the top of the tower.
Whenever lightning strikes a tower, an enormous amount of damage is created. Typically, the electronic device at the top of the tower is completely destroyed by the lightning. Furthermore, the structure of the tower and other associated electronics at the top of the tower can become damaged. Repair efforts on the tower are often time consuming and expensive. Typically, complete replacement of the electronic device at the top of the tower is required. As such, it is very important to develop a device which resists or prevents lightning strikes.
A major problem related to lightning strikes occurs when the lightning strikes a radio, television, or other transmitting and receiving antenna. Typically, these antennas will have coaxial or heliaxial cable extending therefrom. When a lightning strike occurs, the electrical surge will pass through the central conductor of the coaxial cable and also along the conductive shield of the coaxial cable. Ultimately, the lightning wavefront will pass along the coaxial cable to the electronic equipment associated with the broadcasting or receiving operation. As a result, a great deal of damage can occur to such equipment. Conventionally, in the past, a varistor has been connected between the coaxial cable and the antenna and the electronic equipment. Although the varistor can reduce some of the effects of the lightning surge, it has been found generally ineffective in preventing the full and strong effects of the electrical surge from the lightning from affecting the electronic equipment. After a lightning strike, it is often necessary to replace the varistor because of the damage absorbed by the varistor.
In the past, various patents issued relating to such lightning suppression systems. U.S. Pat. No. 5,844,766, issued on Dec. 1, 1998 to L. Miglioli, describes a lightning suppression system for tower-mounted antenna systems. This system includes a directional coupler, a quarter-wavelength stub, a first cylindrical capacitor, a second cylindrical capacitor and a lightning suppression circuit. Each of the cylindrical capacitors has an inner conductor element, an outer conductive tube and a dielectric material. The direction coupler acts to block direct current at low frequency signals from passing therethrough. The quarter-wavelength stub comprises a helicoid and acts to reflect radiofrequency signals back to the transmission line while allowing direct current and low frequency signals to flow therethrough. The first cylindrical capacitor and the second cylindrical capacitor combine to form a low pass filter which allows direct current and low frequency signals to flow through while blocking other signals. The lightning suppression circuit suppresses high voltage direct current and low frequency signals such as those produced by near lightning strikes.
U.S. Pat. No. 5,167,537, issued on Dec. 1, 1992, to Johnescu et al., describes a high density contact assembly capable of low working voltage and high energy handling capacity, including lightning suppression. The contact assembly employs a multi-layered varistor as the transient suppression device. The varistor is mounted in a notch in the contact and connected to ground by way of a ground sleeve. An insulator sleeve separates the ground sleeve from the contact. Both the insulator sleeve and the ground sleeve include a gap or groove extending the length of the sleeve to permit the sleeves to be snapped onto the contact and aligned without the need for additional adhesive staking operations.
U.S. Pat. No. 5,694,286, issued on Dec. 2, 1997 to the present inventor, describes a lightning protection apparatus having a tower which is grounded grounded to the earth, an electronic device mounted onto the area adjacent a top of the tower, and a negative ion production device electrically connected to the top of the tower. The negative ion production device serves to produce solely negative ions around and over the electronic device. An auger rod engages the earth so as to be conductively connected to the earth, and an electrical line serves to connect the auger rod to the tower. A shield member is connected to the tower and extends over the electronic device. The negative ion production device is connected to the shield member so as to pass negative ions through the shield member. The negative ion production device can be one or more batteries that are connected together and have a negative terminal connected to the tower and a positive terminal connected to the electronic device.
It is an object of the present invention to provide a lightning suppression system which prevents lightning strikes from adversely affecting radio, television or other transmitting and receiving equipment.
It is another object of the present invention to provide a lightning suppression system which cushions the effects of lightning strikes upon coaxial or heliaxial cable.
It is still object of the present invention to provide a lightning suppression system which will cushion the effects of lightning from destroying the varistor connected to the electronic equipment.
It is a further object of the present invention to provide a lightning suppression system which lightning suppression system which is easy to install, relatively inexpensive and easy to manufacture.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a system for suppressing the effects of lightning comprising an antenna, a cable extending from the antenna, an enclosure having an interior volume, a coil of conductive wire received within the interior volume of the enclosure, and an item of electronic equipment suitable for receiving from or transmitting through the antenna. The coil has a first lead and a second lead extending outwardly of the enclosure. The first lead is connected to the cable extending from the antenna. The second lead is connected to the electronic equipment. A conductive grit fills a portion of the enclosure. This conductive grit is steel shot.
A grounding rod is electrically connected to the cable, the enclosure and to the electronic equipment. The grounding rod includes a central shaft and a plurality of vanes extending radially outwardly from the central shaft. The central shaft and the plurality of vanes are formed of a conductive material.
The cable is a coaxial or heliaxial cable having a central conductor and an outer conductive shield. The coaxial cable has a connector affixed to an end thereof. The coil of conductive wire is a coaxial or heliaxial line affixed to the connector of the cable. A conductive line is interconnected to the connector of the cable and to the grounding rod. A varistor is connected to the second lead of the coil. The electronic equipment is connected to the varistor.
The grounding bus has a first conductive line connected to the cable, a second conductive line connected to the enclosure and a third conductive line connected to the electronic equipment. The grounding rod has a conductive line connected to the grounding bus. The varistor also has a conductive line connected to the grounding bus.
When a lightning strike occurs, the lightning wavefront will travel around the central conductor and the outer conductive shield of the coaxial cable. This will pass along the coil of conductive wire within the enclosure. The relationship between the coil of conductive wire and the conductive grit within the enclosure will act as a polyphaser suppressor so as to absorb the shock of the lightning, to cushion the effects of the lightning and to dump the lightning to ground.